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Orographic Instability of Nonsymmetric Baroclinic Flows and Nonpropagating Planetary Waves

P. CessiCenter for Meteorology and Physical Oceanography, Massachusetts Institute of Technology, Cambridge, MA 02139

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A. SperanzaCNR-FISBAT, Bologna, Italy

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Abstract

The theory of the baroclinic instability of a nonsymmetric basic state in the presence of shallow sinusoidal topography is analyzed. The limiting case of vanishing topography (instability of a baroclinic Rossby wave) is also critically reexamined as far as some properties, potentially relevant for an explanation of the nonpropagating variance of the westerlies, are concerned.

Orographic instabilities modified by the nonhoinogeneity of the basic state are found. The unstable perturbations display properties that resemble those typical of the observed long-period variability of extratropical winter circulation in the Northern Hemisphere. Some possible physical implications of the existence of such instabilities in the context of the theory of the atmospheric circulation are suggested.

Abstract

The theory of the baroclinic instability of a nonsymmetric basic state in the presence of shallow sinusoidal topography is analyzed. The limiting case of vanishing topography (instability of a baroclinic Rossby wave) is also critically reexamined as far as some properties, potentially relevant for an explanation of the nonpropagating variance of the westerlies, are concerned.

Orographic instabilities modified by the nonhoinogeneity of the basic state are found. The unstable perturbations display properties that resemble those typical of the observed long-period variability of extratropical winter circulation in the Northern Hemisphere. Some possible physical implications of the existence of such instabilities in the context of the theory of the atmospheric circulation are suggested.

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